Cochlear hair cells respond to weak stimuli at very high frequencies. Since the cutoff frequency of the hair cell membrane can be well below that of the stimulus the cell must function as an envelope detector. Envelope detection requires a nonlinear element. This nonlinear element could be present as an integral part of the transduction process or in a subsequent stage. The existing literature indicates the presence of voltage-dependent processes in hair cells of several vertebrate and invertebrate species. These processes may play an important role in both envelope detection and in the excellent sensitivity of cochlear hair cells. The goal of the proposed work is to separate and quantify those phenomena occurring at or before the transduction stage from those occurring in other portions of the hair cell membrane. We propose to voltage-clamp the cochlear sensory epithelium in situ in order to study the receptor currents flowing thrugh the hair cells. In addition, we propose to use cochlear efferent stimulation in an effort to separate the contributions of the inner and outer hair cells. The voltage-clamp technique will also allow us to study voltage-dependent currents from the stria vascularis which may be related to the active processes which maintain the large ionic gradient across the organ of Corti.